| y-MnFe alloys, which can show macro-strain induced by a magnetic field, are anti-ferromagnetic at room temperature. The research on the anti-ferromagnetic shape memory alloys, comparing with the ferromagnetic shape memory alloys, was rarely reported. So, it is very useful to investigate the mechanisms of magnetic field induced strain and its influencing factors in y-MnFe alloys.In this paper, the effects of Mn content on the phase transition, microstructure and magnetic-field-induced strain (at the low magnetic field from OT to IT) in Mn-Fe-based alloys(CMn≥70at%) are investigated by means of XRD, energy spectrum analysis, microstructure observation, DSC and resistance strain gauge method. In the meantime, the effects of aging, and addition of Ni element on the microstructure, structure and magnetic-field-induced strain(O-1T) of Mn7oFe25Cu5 alloy were also explored.The structure of Mn-Fe alloy(CMn=70at%) is y single phase and the fcc(γ)→fct (y') martensitic transformation which increases with the increase of Mn content occurs in Mn-Fe alloys(CMn>70at%) after solution treatment. But MFIS of Mn-Fe alloys(CMn>70at%) are lower than Mn-Fe alloy(CMn=70at%) at the low magnetic field. Antiferromagnetic transition in Mn-Fe alloy(CMn=70at%) trigger formation of microtwins which increases its MFIS properties, at last the MFIS of alloy reaches its maximum value of 124ppm.Unlike medium Mn content Mn-Cu alloy, spinodal decomposition does not occur in Mn-Fe alloys. As a result, structure and MFIS of Mn7oFe25Cu5 alloy reveal small changes after aging at 450℃for 3～9h. But when aging at 500℃for 12～15 h, there is a large number of a-Mn phase separating out, which degrading the MFIS of alloy.Mn7oFe2oNi10 is y single phase after 10at% Ni element is added. And the fcc(γ)→fct(γ') martensitic transformation occurs in MngoFe10Ni10 alloy after solution treatment, just as Mn-Fe alloys(CMn>70at%), but its transformation level is lower. Compared with Mn-Fe(Cu) alloys, magnetic-field-induced strain of them is lower. |
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